The anisotropic conduction sheet is employed in a final conducting test step of a semiconductor device which has been more and more highly integrated, and employed in an electrical connection between the semiconductor device and a printed circuit board. Various types of anisotropic sheets have been proposed and some of them are practically used, but on the whole anisotropic sheets may be classified into two groups. One of the types is called a pressure sensitive conductive rubber. As shown in FIG. 6, such sensitive conductive rubber is constituted by dispersing fine particles 62 formed out of a conductive material in a rubber 61. When the rubber 61 is compressed, the fine particles 62 are contacted each other, so that the rubber 61 becomes conductive (conventional example 1). The idea of the above-mentioned conductive rubber is rather old one, as you can find such idea in a patent application filed in 1973 and granted as a patent right (see Japanese patent application published No. 56-48951). Afterward various efforts have been made to disperse conductive fine particles as uniformly as possible so that the pressure sensitive conductive rubber has been practically used.
As shown in FIG. 7, another type of the anisotropic conductive sheets comprises a soft rubber 71 and gold plated fine metal wires 73 which are densely arranged in the soft rubber 71 (conventional example 2). Since solder bumps of a semiconductor package are pressed against the anisotropic conductive sheet in order to make the semiconductor package electrically conductive, gold plated fine metal wires vertically arranged in the soft rubber are inappropriate, so that an anisotropic conductive sheet having an offset arrangement such that metal wires are slantingly arranged in the soft rubber has been practically used and now it is supposed to be used more frequently.
Since the number of pins of semiconductor packages have been increasing due to the fact that semiconductor devices have been more densely integrated, solder bumps have been employed in most of the semiconductor packages in place of the pins. When heights of the solder bumps with good precision are attempted to manufacture, costs will be increased remarkably high, so that the heights the solder bumps are controlled within a predetermined error. Such solder bumps can not attain good electrical contacts with electrodes arranged on a flat plane, so that the semiconductor packages can not inspected perfectly. Therefore, flexibility as well as a reliable conductivity are required in the anisotropic conductive sheet. Since the solder bumps are pressed against the anisotropic conductive sheet, vertically arranged fine metal wires are inappropriate, so that slantingly arranged fine metal wires are employed instead in order to reduce pressures between the solder bumps and the anisotropic conductive sheet.